In general, methods of manufacturing a stator coil for an electric rotating machine are sorted as a individual impregnation method and a global impregnation method. The individual impregnation method includes the steps of impregnating only a stator coil; heating and curing the resin in a heated press; and joining the stator coil with a slot of stator core; and winding wire. The global impregnation method includes the steps of joining a stator coil, which is not impregnated with the resin, to a slot of stator core; winding wire; and impregnating with the resin which is then cured. The global impregnation method causes the stator coil and the stator core to be strongly secured to each other. Therefore, the overall body of the winding has great mechanical rigidity, causing the thermal resistance between the stator coil and the stator core to be reduced as compared with that realized with the individual impregnation method. As a result, a rise in the temperature of the stator coil caused from heat produced from a conductor within stator coil during the operation can efficiently be prevented as compared with the individual impregnation method. If the stator coil is manufactured by the global impregnation method, an advantage can be realized in that the manufacturing process can be shortened because only one execution of each of the impregnation and curing processes is required.
On the other hand, size reduction and large capacity of the electric rotating machine, which is manufactured by the global impregnation method, have caused the current density of the conductor of the stator coil to be raised. Thus, the heating value of the conductor within stator coil is increased. In general, when an electric rotating machine rotates, heat generated in the conductor within stator coil serving as a driving force causes shearing stress to occur between the surface of the stator coil and the slot of stator core owing to the difference in the coefficients of thermal expansion. Therefore, the heating of the conductor within stator coil is increased, causing the shearing force to be enlarged. Thus, there arises a problem in that defects, such as separation and cracks, occur in ground wall insulation of stator coil.
On the other hand, as a method for shear stress relaxation occurring in the ground wall insulation of a stator coil, a contrivance has been disclosed by the applicant of the present invention in Japanese Patent Application No. 8-120222, in which an non-adhesive tape is wound around the outer surface of the ground wall insulation of the stator coil.
FIG. 9 is a diagram showing the conventional stator coil, in which an outlet portion of the slot is illustrated, which is included in a structure in which the stator coil is employed in a high-voltage electric rotating machine. Referring to the drawing, reference numeral 1 represents a stator core, 13 represents a stator coil, 13a represents an upper coil, 13b represents a lower coil, 3 represents a conductor within the stator coil, 4 represents a ground wall insulation of the stator coil, 5 represents a wedge, 6 represents an insulating spacer between upper and lower coil, 7 represents a slot of stator core, 8 represents a conductive-and-non-adhesive tape, and 9 represents a semiconductive tape.
FIG. 10 is a diagram showing a portion of the conductive-and-non-adhesive tape 8 in the lengthwise direction. One of the surfaces of the conductive-and-non-adhesive tape 8 is subjected to a surface treatment by corona discharge. FIG. 11 is a diagram showing a state of accommodation in which the conventional stator coil has been accommodated in the slot of stator core 7.
That is, a mica tape is wound around the conductor 3 within stator coil several times so that the insulating layer 4 of the stator coil is formed. Then, a conductive-and-non-adhesive tape 8 (see FIG. 10) having one side subjected to the surface treatment by corona discharge is obtained. The conductive-and-non-adhesive tape 8 is half lap wound around the surface of the ground wall insulation the stator coil such that a surface 14 of the conductive-and-non-adhesive tape 8 subjected to the corona faces the insulating layer 4 of the stator coil to the ground. Then, the semiconductive tape 9 is half lap wound around the conductive-and-non-adhesive tape 8.
The stator coil 13 is inserted into the slot of stator core 7, and then the wedge 5 is driven to secure the stator coil 13. Then, the stator coils 13 are electrically and mechanically connected to one another by connection between coils. Then, impregnation and hardening of the resin are performed.
The surface of the conductive-and-non-adhesive tape 8 subjected to the conductive-and-non-adhesive tape 8 and the surface of the insulating layer 4 of the stator coil to the ground are strongly bonded to each other by the impregnation resin. Another surface of the conductive-and-non-adhesive tape 8 which is not subjected to the surface treatment by corona discharge and the semiconductive tape 9 are separated from each other if a shearing force of adequate magnitude is exerted.
Therefore, the shearing force produced between the insulating layer 4 of the stator coil to the ground and the slot of stator core 7 can be moderated because the semiconductive tape 9 and the conductive-and-non-adhesive tape 8 are separated from each other. As a result, no shearing force is exerted on the insulating layer 4 of the stator coil to the ground. As a result, separation and cracks in the insulating layer 4 of the stator coil to the ground can be prevented.
Since the conductive-and-non-adhesive tape 8 establishes the electrical connection between an stator core 1 and the stator coil 13, production of a surface corona can be prevented.
However, the foregoing stator coil of the electric rotating machine incorporates a conductive-and-non-adhesive tape 8 constituted by a fluorine-containing film. The film has poor wettability with respect to the impregnation resin. As shown in FIG. 11, lapped portions of the films encounter a sealing effect owning to close contact between the films. As a result, the impregnation characteristic of the impregnation resin with respect to the insulating layer 4 of the stator coil deteriorates. Therefore, portions which are not impregnated with the resin are easily formed in the insulating layer 4 of the stator coil. As a result, there is apprehension that the mechanical strength and the electric characteristics of the stator coil deteriorate.
To solve the above mentioned problem, an object of the present invention is to obtain a stator coil for a electric rotating machine, which does not deteriorate the impregnation characteristic of the resin with respect to the ground wall insulation of stator coil, which is able to prevent generation of a surface corona while a smooth releasing characteristic is being maintained, which is able to prevent occurrence of a surface corona and which is able to maintain excellent characteristics for a long time.